1. CS 432 Object-Oriented Analysis and Design*
07/16/96
CS 432 Object-Oriented Analysis and Design
Week 6
Design Patterns
Architecture Designs *

3. Design Principles-Protection From Variations
Parts of a system that are unlikely to change are segregated from those that will
Drives the multilayer design pattern
Stable business logic can be protected from variations in the user interface
Changes in the business logic are isolated to the controller class

4. Design Principles-Indirection
Indirection is an implementation of the protection from variations principle
Decouples classes or other system components by placing an intermediate classes between them
Used in many corporate security systems between an internal network and the Internet
A proxy server catches all incoming messages and redistributes them to the recipients

5. Importance of Design Patterns
Standard design templates can speed OO design
Patterns can exist at different levels of abstraction
At the most concrete level, a class definition with code
At the most abstract level, an approach to a problem
Patterns should contain five main elements
Pattern name, problem, solution, example, benefits and consequences

6. Pattern description
for the controller pattern

7. Basic Design Patterns
The authors of Elements of Reusable Object-Oriented Software (referred to as the Gang of Four) developed a basic classification scheme for patterns (Figure 9-7)
The 23 GoF patterns are some of the most fundamental and important patterns in use
Scores of other patterns have been defined
For example, both Java and .NET have sets of enterprise patterns

8. Classification of design patterns

9. Singleton Pattern
For classes that must have only one instance, but need to be invoked from several classes and locations within the system
The class itself controls the creation of only one instance
A static variable of the class refers to the object that is created
A class method instantiates the object on the first call, and returns a reference to the object on subsequent calls

10. Singleton Pattern

11. Singleton
pattern
template

12. Adaptor Pattern Plugs an external class into a system
Converts the method calls from within the system to match the method names in the external class
A standard solution for protection from variations
Insulates the system from frequently changing classes
An interface is frequently used to specify and enforce the use of correct method names

13. Adapter Pattern

14. Adapter pattern template

15. Design Activities in the UP Life Cycle

16. Design the Support Services Architecture and Deployment Environment
Three organizational dispositions to new systems
Integrate new systems into existing systems
Install support services for the first time
Replace existing systems
Design issues for all organizations
Reliability
Security
Throughput
Synchronization

17. Design the Software Architecture
Software architecture refers to the “big picture”
Two important aspects
Division of software into classes
Distribution of classes across processing locations
Modify class diagrams into software classes
Determine where classes and objects execute
Determine whether they will be distributed
Determine communication methods
Select programming language(s) to write classes

18. Design Use Case Realizations
Use case realizations offer a lower-level view
Two-tiered focus
Class interactions supporting a particular use case
Interactions among software, users, and external systems
Design typically spread over many iterations
UML design class diagrams and interaction diagrams document design

19. Design the Database Designing database as a key design activity
Physical model of database based on class diagram
Physical model describes relational or OO database
Some technical issues
Performance, such as response time
Integration with existing databases
Legacy databases

20. Design the System and User Interfaces
System interface issues
Different types of systems will interface
Systems interact with internal and external users
User interface issues
User capabilities and needs differ widely
User interacts with the system in different ways
Approaches to interface vary by system
Has nature of interface emerged from earlier models?

21. Design the System Security and Controls
User-interface controls limit access to authorized users
System interface controls protect system from other systems
Application controls record transactions and validate work
Database controls ensure data protected from unauthorized access and accidental loss
Network controls protect network communication

22. Design Activities and the UP
Focus in early iterations of elaboration phase
System architecture and databases
Evenly distributed throughout project
Detailed design activities
Criteria analyst uses to schedule design activities
Experience
Forecasting capabilities
Every design impacts other parts of system

23. Single-Computer and Multitier Architecture
Single-computer architecture
Single system attached to peripheral devices
PC and mainframe applications qualify
Advantages: easy to design, build, operate, maintain
Disadvantages: capacity limits

24. Single-computer, Clustered, and Multicomputer Architectures

25. Single-Computer and Multitier Architecture (continued)
Multitier architecture (multiple computer systems)
Clustered architecture
Group of computers logically operate as one
Nodes from same manufacturer and model family
Multicomputer architecture
Cluster whose nodes are optimized or specialized
Hardware and operating systems may be dissimilar

26. Centralized and Distributed Architecture
Centralized architecture
Deploys computer systems in single location
Used for large-scale processing applications
Constraint: geography
Implements subsystems in larger information system
Distributed architecture
Software/data spread across systems and locations
Relies on communication networks to interconnect

27. Client/Server Architecture
Client/server architecture tiers
Client: requests resources or services from a server
Server: manages information system resources
Architectural issues for client/server software:
Decomposing software into client and server programs (objects)
Determining where clients and servers will execute
Describing interconnection protocols and networks

28. Client/Server Architecture with a Shared Database

29. Client/Server Architecture (continued)
Client and server communicate via well-defined protocols over a physical network
Client/server architecture advantages
Location flexibility, scalability, maintainability
Client/server architecture disadvantages
Additional complexity, potential poor performance, security issues, and reliability 

30. Interaction Among Multiple Clients and a Single Server

31. Three-Layer Client/Server Architecture
Variant of client/server architecture
Divides application software into independent processes
Three-layers
The data layer
The business logic layer
The view (presentation) layer
Three-tier architecture advantages
Additional flexibility and reliability

32. Three-Tier Logical Layers

33. Three-Tier Architecture

34. Four-Tier Architecture

35. Model-View-Controller (MVC) Design Pattern or Framework

36. Middleware Middleware Common types of middleware
Connects parts of an application
Enables requests and data to pass among them
Common types of middleware
Teleprocessing monitors
Transaction processing monitors
Object request brokers (ORBs)
Each type of middleware has its own set of protocols

37. Differences between client/server and Internet systems

38. Web Client/Server Architecture

39. Internet and Web-Based Software Architecture
Web is complex example of client/server architecture
Web resources are managed by server processes
Clients are programs that send requests to servers
Web protocols define valid resource formats and communication standards
Web-like capabilities embedded in ordinary applications
Web-oriented client/server architecture: service-oriented architecture (SOA)  

40. Internet and Web-Based Software Architecture (continued)
Flexibility is the key to the Internet alternative
Accessibility, low cost communication, widely used standards
Disadvantages of Web technologies
Security, reliability, throughput, and volatile standards
The key architectural design issues
Defining client and server processes or objects
Distributing processes across hardware platforms
Connecting processes

41. Simple Internet Architecture
Used for viewing static information
The browser component executes on the client computer
The Internet server component executes on the server computer
Pages reside on the server and are sent to the browser for display
Program logic is inserted through scripting languages (JavaScript, VBScript), applets, or other controls

42. Simple Internet architecture

43. Two-layer Architecture
Primarily captures information from the user and updates the database
The domain layer and data access layer are usually combined
Input data is sent to a CGI or an application server
The user-interface classes often contain the business logic and data access
Processing takes place with servlets (Java) or code behind classes (.NET)

44. Two-layer Internet architecture

45. Three-layer Architecture
Separates domain layer and data access layers
Necessary for systems with complex business logic or multiple user interfaces
Using CGI
Provide a use case controller for each form that distributes messages to the individual objects of the system.
Using an application server
Java tools: Java Server Pages and servlets
.NET tools: Common Runtime Language and code behind classes

46. Internet architecture
Three-layer
Internet architecture

47. Invoking a Web service

48. Designing Enterprise-level Systems
Enterprise-level systems share components among multiple people or groups in an organization
Enterprise-level systems almost always use multiple tiers of computers
Can be client/server network-based or Internet based
Designed with deployment diagrams
A type of implementation diagram that shows physical components across different locations